Of course, the down side with dictionarys as opposed to people is that they tend to give the litteral translation and not the best word to be used

Anyway, while in Dutch the word "donker" means dark, I am not sure that is the word you are looking for. The Dutch word "donker" is used mainly when there is a lack of light or when it is darker variation of a color. When you use "a dark night" to describe a somewhat threatening mood the word "duister" is probably much better. This especially true when you want the tranlation of darkness, because that would be "duisternis". When translating a word you should really give the context in which you want to use it.

Other words for darkness on EN world is ofcourse Shadow of My former Self

Anyway, as Madfox already stated there are other words for the Dutch donker. The words duister and duisternis are very good. But that's not all. How about a not very common (regional) word for duisternis: Deemster, it is derived from the Latin tenabrae or from the old Greek themeros; BTW deemstering means twilight.

For shadow I have found this:Immersie, it's the start of the shadow of one celestial body on another .Lommer, it's the shadow of the foliage of a tree and shrubs.Lommering, old fashioned word.Nevelbeeld the image made on a mist by the shadow of the observer. (nevel means mist and, beeld means image)Schad, also a regional word, it also means the reflection in water or ice.Scheem, another regional word, it's also the shadow of a dead person, (kind of ghost I guess). Schemering is also another word for twilight.Schemer is also a word for the time between light and dark.

And there are the words halfduister, halfdonker and halflicht (half means half, licht means light).

<i>ignotus</i> means something like ignored or overlooked, used specifically to indicate forgiveness for some sort of transgression. Obscure would be a very unusual translation of it.
Obscure in a visual sense is, not surprisingly, <i>obscurus</i>, c.f. French <i>obscure</i>, Italian <i>oscuro</i>.
<i>ater</i>, not "atrer", the basic meaning is dull/flat black
<i>acerbus</i> means sharp or bitter, has nothing to do with darkness. I assume this was listed as a synonym for "dark" in the metaphorical sense as in "a dark mood."
Also:
<i>tenebra/tenebrae</i> = shadow, darkness
<i>occultus</i> = concealed, secret
<i>opacus</i> = shaded, dark
<i>caligo</i> = mist, gloom, darkness

The 'Ó' letter isn't pronounced any different from a normal 'a', it just means that the stress is on the last syllable. All Italian vowels are always pronounced in almost the same way, regardless of which word they're in or which position they occupy, so pronounce shouldn't be a problem.